[en] In recent years precision cosmology has become an increasingly powerful probe of particle physics. Perhaps the prime example of this is the very stringent cosmological upper bound on the neutrino mass. However, other aspects of neutrino physics, such as their decoupling history and possible non-standard interactions, can also be probed using observations of cosmic structure. Here, I review the current status of cosmological bounds on neutrino properties and discuss the potential of future observations, for example by the recently approved EUCLID mission, to precisely measure neutrino properties.

[en] We update the bounds on fermions with electric charge epsilon e and mass m_ε. For m_ε lsim m_e we find 10^(-15) lsim ε<1 is excluded by laboratory experiments, astrophysics and cosmology. For larger masses, the limits are less restrictive and depend on m_ε. For milli-charged neutrinos, the limits are stronger, especially if the different flavors mix as suggested by current experimental evidence. (author)

[en] If the diffuse extragalactic gamma ray emission traces the large scale structures of the universe, peculiar anisotropy patterns are expected in the gamma ray sky. In particular, because of the cutoff distance introduced by the absorption of 0.1-10 TeV photons on the infrared/optical background, prominent correlations with the local structures within a range of few hundreds Mpc should be present. We provide detailed predictions of the signal based on the PSCz map of the local universe. We also use mock N-body catalogues complemented with the halo model of structures to study some statistical features of the expected signatures. The results are largely independent from cosmological details, and depend mostly on the index of correlation (or bias) of the sources with respect to the large scale distribution of galaxies. For instance, the predicted signal in the case of a quadratic correlation (as it may happen for a dark matter annihilation contribution to the diffuse gamma flux) differs substantially from a linear correlation case, providing a complementary tool to unveil the nature of the sources of the diffuse gamma ray emission. The chances of the present and future space and ground based observatories to measure these features are discussed

[en] In a recent Letter we presented the first numerical treatment of the full set of Boltzmann equations for the evolution of an MeV Majorana τ neutrino in the early Universe. The conclusion was that mass limits from big bang nucleosynthesis were significantly weakened compared to previous investigations. An error in our numerical code unfortunately invalidates the results. We present here the correct results that lead to a strengthening of earlier mass limits based on the integrated Boltzmann equation. copyright 1996 The American Physical Society

[en] The primordial abundance of long-lived heavy Majorana neutrinos is calculated from the full Boltzmann equation. Inclusion of scattering reactions drastically changes the predicted abundance of a heavy neutrino species. This loosens the well known mass constraint on MeV neutrinos from big bang nucleosynthesis, and allows for the existence of a Majorana τ neutrino with mass m_ντ≥11 MeV. Further experimental efforts are therefore needed to investigate the range 11≤m_ντ≤24 MeV. Some interesting cosmological consequences of an MeV ν_τ are also pointed out. copyright 1996 The American Physical Society

[en] The Pierre Auger Collaboration has reported a correlation between ultrahigh energy cosmic rays (UHECR) and nearby active galactic nuclei (AGN) within ∼75 Mpc. Two of these events fall within 3 degrees from Centaurus A (Cen A), the nearest AGN, clearly suggesting that this object is a strong UHECR emitter. Here we pursue this hypothesis and forecast the expected rate of ultrahigh energy neutrinos in detectors like IceCube. In our baseline model we find a rate of ∼0.4-0.6 yr^-1 events above a threshold of 100 TeV, the uncertainty of which is mainly related to the poor knowledge of the physical parameters of the source and details of the model. This situation will improve with detailed high energy gamma ray measurements of Cen A by the upcoming Gamma Ray Large Area Space Telescope (GLAST) satellite. This would make Cen A the first example where the potential of high energy multimessenger astronomy is finally realized.

[en] We present a calculation of a neutrino decay scenario in the early Universe. The specific decay is ν₂→ν₁+φ, where φ is a boson. If there is a neutrino mass hierarchy, m_νeν_μν_τ, we show that it is possible to generate stimulated decay and effects similar to atomic lasing without invoking new neutrinos, even starting from identical neutrino distributions. Under the right circumstances the decay can be to very low-momentum boson states thereby producing something similar to a Bose condensate, with possible consequences for structure formation. Finally, we argue that this type of decay may also be important elsewhere in early Universe physics. copyright 1997 The American Physical Society

[en] An expression for the average redshift drift in a statistically homogeneous and isotropic dust universe is given. The expression takes the same form as the expression for the redshift drift in FLRW models. It is used for a proof-of-principle study of the effects of backreaction on redshift drift measurements by combining the expression with two-region models. The study shows that backreaction can lead to positive redshift drift at low redshifts, exemplifying that a positive redshift drift at low redshifts does not require dark energy. Moreover, the study illustrates that models without a dark energy component can have an average redshift drift observationally indistinguishable from that of the standard model according to the currently expected precision of ELT measurements. In an appendix, spherically symmetric solutions to Einstein's equations with inhomogeneous dark energy and matter are used to study deviations from the average redshift drift and effects of local voids

[en] We study the difference between thermally produced fermionic and bosonic hot dark matter in detail. In the linear regime of structure formation, their distinct free-streaming behaviours can lead to pronounced differences in the matter power spectrum. While not detectable with current cosmological data, such differences will be clearly observable with upcoming large scale weak lensing surveys for particles as light as m_HDM ∝ 0.2 eV. In the nonlinear regime, bosonic hot dark matter is not subject to the same phase space constraints that severely limit the amount of fermionic hot dark matter infall into cold dark matter halos. Consequently, the overdensities in fermionic and bosonic hot dark matter of equal particle mass can differ by more than a factor of five in the central part of a halo. However, this unique manifestation of quantum statistics may prove very difficult to detect unless the mass of the hot dark matter particle and its decoupling temperature fall within a very narrow window, 1≤m_HDM/eV≤4 and g_*≤30. In this case, hot dark matter infall may have some observable consequences for the nonlinear power spectrum and hence the weak lensing convergence power spectrum at l ∝ 10³ → 10⁴ at the percent level. (orig.)

[en] We study models in which neutrino masses are generated dynamically at cosmologically late times. Our study is purely phenomenological and parameterized in terms of three effective parameters characterizing the redshift of mass generation, the width of the transition region, and the present day neutrino mass. We also study the possibility that neutrinos become strongly self-interacting at the time where the mass is generated. We find that in a number of cases, models with large present day neutrino masses are allowed by current CMB, BAO and supernova data. The increase in the allowed mass range makes it possible that a non-zero neutrino mass could be measured in direct detection experiments such as KATRIN. Intriguingly we also find that there are allowed models in which neutrinos become strongly self-interacting around the epoch of recombination.